The Radiant Rainmaker is a mount which can be obtained through completing Badges. Players would have to get the Diamond Total Days Badge (Logging in for a total of 180 days) to obtain this mount (based off of the 6/26/15 livestream).

Trivia

This mount, along with the Infineon Charger and a collection of other Bull Mounts are all created by Screamheart. These mounts can be seen in the original thread here.